Bug 1860612 [wpt PR 42689] - Implement an unprefixed mask-composite property, a=testonly

Bug 1860612 [wpt PR 42689] - Implement an unprefixed mask-composite property, a=testonly

Automatic update from web-platform-tests
Implement an unprefixed mask-composite property

This patch adds an updated and unprefixed mask-composite property behind
the experimental flag CSSMaskingInterop. In addition to unprefixing, the
patch changes the supported values of only the unprefixed property to
match https://drafts.fxtf.org/css-masking/#the-mask-composite:
  add (source-over)
  subtract (source-out)
  intersect (source-in)
  exclude (xor)

Bug: 1418401
Change-Id: I100546a799d86f26d06d52a6ca55d9ced93d766b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4953599
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Traian Captan <tcaptan@chromium.org>
Auto-Submit: Philip Rogers <pdr@chromium.org>
Commit-Queue: Traian Captan <tcaptan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1213850}

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wpt-commits: d8226bbcf1d1fc860f648b8281f498e666d72af7
wpt-pr: 42689